Apparently it is not possible for the moment to specify a custom suffix to the complete URL of a DoH server (for example, with a AdGuard server, I cannot append a client identifier such as dns.contoso.com/dns-query/my-client, while dns.contoso.com is working fine).

Will stick to DoT for the moment :)

EDIT : ok so only 'dns.google' or 'cloudflare-dns.com' are supported right now, other domains are still using DoT. Pretty useless feature then :(